1. Field of the Invention
The present invention relates to a method of manufacturing a synthetic fiber bundle for use in cosmetic brushes, paint brushes, and writing brushes.
2. Prior Art
Conventionally, the head of brushes of this type was manufactured by manually tying up animal hair such as horse hair, wool and pig hair, at its end with a wire or a thread, etc., to obtain a bundle and, if necessary, cutting and shaping the thus obtained bundle so that its cross section takes a prescribed shape or shaping the bundle with a highly viscous paste. This conventional method is extremely labor-saving and low in production efficiency. In addition, it is inconvenient because in pasting it up as described above, the method requires great skill to provide a proper degree of penetration of the paste solution.
On the other hand, to solve recent problems with respect to not only a limit in resources of animal hair but also sanitation and environments in an animal hair treatment, substitution of an animal hair-made head by a synthetic resin-made head has been used. Moreover, methods for more effectively manufacturing such heads profitably employing the properties of synthetic fibers have also been investigated.
For example, the present inventor used thermoplastic synthetic fibers such as nylon fibers made by a melt spinning method to obtain a fiber bundle for use as material for one such head, after which the thus obtained bundle was heated at one end surface to fuse the fibers of the bundle together at that end instead of tying up or pasting up the fibers at that end. It was proposed to use the bundle so heat treated as a head of a brush.
Since, however, this conventional method comprises heating one end surface of the fiber bundle by contacting a heater such as an electrical heater plate with the bundle end surface or allowing the former to approach the latter, the thickness of the fused layer of the bundle is non-uniform due to slight unevenness of the original bundle end, whereby the thus fusion treated fiber bundle or head longitudinally cracks in the thinner part of the fusion bonded layer. To obtain a fusion bonded layer having a proper thickness of the fusion bonded layer, great skill is undesirably required for setting the temperature of the electrical heater plate, its contact pressure against the bundle end surface, the distance between the heater plate and the bundle end surface, the heating time, etc. With an apparatus for implementing such a conventional method it takes about 90 seconds to complete the fusion bonding and about 100 seconds to manufacture one head. Accordingly, there can be obtained only thirty six heads per hour, or only two hundred and eighty-eight bundles per day asuming the working time to be eight hours per day. This low fusion bonding rate will result in a decrease in productivity since one worker is required to operate one device for carrying out the fusion bonding and hence such a method is not deemed to be a satisfactory.
Hereupon, the present inventor intended to improve the method described above; he devised and implemented a method of forming a fiber bundle for use as a brush head which comprises (1) providing a fiber bundle, called "hank", having a diameter of about 50 mm and a length of about 1.5 m formed by tying up, for example, fibers for wigs or the like and then winding the thus provided fiber bundle with paper in the same manner as a bandage is wound so as not to permit the bundle to have tendency to bend, (2) cutting the bundle to obtain a plurality, for example several tens, of bundle pieces of suitable length, (3) contacting the surface of one end of the pieces with a heat source such as a heated metal plate or allowing it to approach the heated plate to fuse the surface, (4) cooling the fused surface for solidification and (5) then separating the bundle pieces or heads in each of which the tips of the fibers have been fusion bonded together, from each other. According to this method, the fusion bonding time for each fiber bundle is merely about 3 seconds, assuming that the number of fiber bundles to be fusion bonded simultaneously is 30.
However, the above method took much time to separate the resulting heads from each other. Moreover, this method is not too satisfactory one since its production rate is low as in the case of the previously mentioned method by which brush heads are produced one by one. Furthermore, when the method is applied to synthetic fibers not having sufficient thermal stability, fusion and thermal decomposition of the fibers, though depending on the rate of raising the temperature, will simultaneously take place whereby a strong fusion bonded surface cannot be formed.
Synthetic fibers, such as modacrylic fibers which are obtained from a copolymer of vinyl chloride and acrylonitrile, obtained by means of a solution spinning method are excellent in surface condition and touch as compared with nylon fibers, etc., and in particular the modacrylic fibers, etc., resemble wool in touch and are suitable as a substitute for animal hair. Therefore, it is earnestly desired in this field to develop a method of manufacturing fiber bundles which is applicable to synthetic fibes having poor thermal stability obtained by means of such a solution spinning method.